I think word of mouth works best. I’m a graphic designer in NYC, but I did a job for client in LA and we used this printer. I was happy with both the knowledgeable staff and the quality of the printed product:

I work with Southern California graphics in Culver City a lot. They’re a full-service print shop. They have a new digital press that will make printing a small-run of business cards pretty cheap, and they’ll print on whatever kind of stock you want. Send an email to Rick rick_h@socalgraph.com or call (310) 559–3600.